Abstract
We developed a temporal population receptive field model to differentiate the neural and hemodynamic response functions (HRF) in the human lateral geniculate nucleus (LGN). The HRF in the human LGN is dominated by the richly vascularized hilum, a structure that serves as a point of entry for blood vessels entering the LGN and supplying the substrates of central vision. The location of the hilum along the ventral surface of the LGN and the resulting gradient in the amplitude of the HRF across the extent of the LGN have made it difficult to segment the human LGN into its more interesting magnocellular and parvocellular regions that represent two distinct visual processing streams. Here, we show that an intrinsic clustering of the LGN responses to a variety of visual inputs reveals the hilum, and further, that this clustering is dominated by the amplitude of the HRF. We introduced a temporal population receptive field model that includes separate sustained and transient temporal impulse response functions that vary on a much short timescale than the HRF. When we account for the HRF amplitude, we demonstrate that this temporal response model is able to functionally segregate the residual responses according to their temporal properties.
Highlights
Over the past 15 years, researchers have characterized the retinotopic organization of the humanlateral geniculate nucleus (LGN) in vivo [1,2,3,4,5]
The use of PD images to guide the drawing of the LGN regions of interest (ROIs) was critical, as the T1-weighted anatomical images did not offer sufficient contrast to identify the boundaries of the LGN
We found that the amplitude maps were consistent across subjects and hemispheres such that the voxels with the largest amplitudes were clustered in the hilum region, the central medioventral portion of each LGN, and that the amplitude decreased towards the dorsolateral aspect of each LGN (Figure 3)
Summary
Over the past 15 years, researchers have characterized the retinotopic organization of the humanLGN in vivo [1,2,3,4,5]. Along with its small size and deep location in the brain, the hemodynamic properties of the LGN have made it difficult to study using functional magnetic resonance imaging (fMRI) techniques. Of particular interest for study in the LGN is the development of methods for functionally segmenting its magnocellular (M) and parvocellular (P) layers. The LGN is somewhat unique in the visual pathway in that there is a clear separation of structure and function at a spatial scale resolvable by contemporary functional imaging techniques. It provides a unique opportunity for developing and testing models of neural function, visual perception, and information flow throughout the brain. One prevailing theory of dyslexia contends that a malfunction in the M system throughout the brain is responsible for the behavioral deficits observed in dyslexics [6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
